How do you enable rigid body physics for a given object in Blender 2.8?
This question is related to How do I add a rigidbody to an object with python?.

In 2.8 you need to use collections, so if you want to add rigid body physics to object my_object for scene 'Scene':

bpy.data.scenes['Scene'].rigidbody_world.collection.objects.link(my_object)


and verify outcome with

my_object.rigid_body is not None